Dialysis is a process for purifying the blood of patients with acute or chronic renal insufficiency. A fundamental distinction is made here between methods having an extracorporeal blood circulation, such as hemodialysis, hemofiltration or hemodiafiltration, and peritoneal dialysis, which does not use an extracorporeal blood circulation.
In hemodialysis, blood in an extracorporeal circulation is passed through the blood chamber of a dialyzer, which is separated from a dialysis fluid chamber by a semipermeable membrane. A dialysis fluid containing the blood electrolytes in a certain concentration flows through the dialysis fluid chamber. The substance concentration of blood electrolytes in the dialysis fluid corresponds to the concentration in the blood of a healthy person. During the treatment, the patient's blood and the dialysis fluid are passed by both sides of the semipermeable membrane, usually in countercurrent at a predetermined flow rate. The substances that are eliminated in urine diffuse through the membrane from the blood chamber into the chamber for dialysis fluid, whereas electrolytes which are present in the blood and in the dialysis fluid at the same time diffuse from the chamber of higher concentration to the chamber of the lower concentration. If a pressure gradient from the blood side to the dialysis side is established on the dialysis membrane, water will diffuse out of the patient's blood, through the dialysis membrane and into the dialysis circulation, i.e., the so-called ultrafiltrate. This process of ultrafiltration leads to the desired withdrawal of water from the patient's blood.
In hemofiltration, ultrafiltrate is withdrawn from the patient's blood by applying a transmembrane pressure in the dialyzer or hemofilter, without any dialysis fluid being passed by the side of the membrane of the dialyzer on the patient's blood side. In addition, a sterile and pyrogen-free substituate solution may also be added to the patient's blood. We speak of predilution or post-dilution, depending on whether this substituate solution is added upstream or downstream from the dialyzer or hemofilter. The mass exchange takes place by convection in hemofiltration.
A combination of hemodialysis and hemofiltration occurs when substituate is added to the patient's blood simultaneously during a dialysis treatment. This form of treatment, which is also known as hemodiafiltration, is also covered by the concepts of hemodialysis, dialysis or dialysis treatment in the following discussion.
It is of crucial importance in a dialysis treatment that the removal of fluid is measured and balanced with great accuracy because there could be serious consequences for the patient even if the withdrawal of fluid is only slightly too great.
This is ensured by the fact that the inflow of dialysate or dialysis fluid into the dialysis fluid chamber and the outflow of dialysis fluid out of the dialysis fluid chamber are controlled separately from one another. The balance between the quantity of fluid added to the dialysis fluid chamber and the quantity of fluid withdrawn from the dialysis fluid chamber at the same time provides a measure of the ultrafiltrate withdrawn from the patient blood.
One possibility for balancing is to use balance chamber pumps based on the principle that a quantity of fluid supplied in an inflow to the dialysis fluid chamber corresponds to a quantity of fluid withdrawn in an outflow out of the dialysis fluid chamber.
For the additional withdrawal of fluid from the patient, another flow path with a delivery device, a so-called ultrafiltration pump, is set up in parallel with the blood chamber. The fluid to be withdrawn is passed through the parallel flow path going past the balance chamber and is measured by the ultrafiltration pump and thus forms a measure of the fluid balance.
Balance chambers have a complex structure and make high demands of the manufacturing tolerance.
As an alternative, the ultrafiltration could be controlled by controlling the flow rate in the inlet line to the dialysis fluid chamber and the flow rate in the outlet line out of the dialysis fluid chamber by pumps which can be controlled independently of one another and are arranged in the inlet line and in the outlet line. In this case, the balancing is performed by flow sensors arranged in the inlet line and the outlet line or by carts, which is associated with a great complexity for the calibration of these sensors or carts.
Therefore the object of the present invention is to overcome at least one of the aforementioned problems and to make available a simple device and a corresponding method for regulating ultrafiltration.